This invention relates to an X-ray computerized tomography apparatus and, more particularly, to an X-ray CT apparatus having a dynamic scanning function for repeatedly obtaining a tomographic image of a region of interest of a living subject under examination.
As a means for observing changes occurring over time in a region of interest of a subject under examination, an X-ray CT apparatus is known which has a dynamic scan function for repeatedly obtaining a tomographic image of the region in question.
The following are methods by which the dynamic scan image can be observed:
(1) Cine display: Tomographic images are displayed continuously frame by frame at a high speed.
(2) Multi-frame display: A plurality of reduced-scale tomographic images are simultaneously displayed on a screen.
(3) Time density curve display: The average value of CT values in an area of interest of a tomographic image is obtained for each of the tomographic images, and this average value is displayed in the form of a graph.
The methods of observation noted above nevertheless entail the following problems:
First, when cine display is employed, quantitative observation is difficult. In addition, it is possible that slight changes may be overlooked, since only a single image can be displayed at a time.
In the case where the multi-frame display is used, changes cannot easily be recognized without simultaneous comparative observation of adjacent tomographic images. Without an image-comparison facility, any observation carried out over an extended period will undoubtedly result is an increase in observer fatigue.
In the case where time density curve display is utilized, CT values can be recognized only for a particular area of interest, with the result that it is difficult to evaluate the overall image.